As well as adjusting individual glyph positions it is also possible to adjust the metrics for an entire font. Within the Metrics tab on the right hand panel in the user interface there is a section called Font Metric Adjustments. Making changes to these values changes to these values causes adjustments to be made to all the glyphs in your font. The result of these changes can be seen in the preview view just as when making individual glyph changes.
At the bottom of this panel are two buttons Reset All Glyph Metrics and Reset All Images. These do exactly what it says on the button and allow you to reset either all your glyphs metrics or images should custom images have been defined.
These buttons are destructive and cannot be undone.